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  • lazar
    Participant
      September 20, 2009 at 5:27 am #2990
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      CAN ANYONE SUGGEST THE STRESSING CALCULATION FOR I GIRDER

      Decipher
      Participant
      Posts: 46
        September 20, 2009 at 8:35 am #3269
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        Rahuman,

        Follow this procedure.

        1. First determine if it is one-end stressing or two-end stressing. The length of the tendon will determine that. Rule of thumb, if it is less than 100 ft, one-end stressing. If longer than that, 2-end stressing. After you know which one, do this.
        You run your stressing and elongation calculations based on 100% of jacking force. You will get an elongation, let's say “E” from whatever software you used. That is between wedges with no seating loss. Then do the following to generate your field table.

        1. For end stressing:
        you first stress 20% of jacking force to remove slack.
        BEFORE LOCK-OFF: (Elongation between wedges + Elongation inside jack + Dead end anchor set) x 0.80
        AFTER LOCK-OFF: (Elongation between wedges + Dead end anchor set) x 0.80 – Live End Anchor Set

        2. if it is 2-end stressing:
        Again you stress the first end only with 20$ to remove slack.
        a. First End Pull:
        BEFORE LOCK-OFF: (Elongation between wedges + Elongation inside jack + Dead end anchor set) x 0.80
        AFTER LOCK-OFF: (Elongation between wedges + Dead end anchor set) x 0.80 – Live End Anchor Set
        b. Second End Pull:
        BEFORE LOCK-OFF: (Elongation between wedges + Elongation inside jack ) x 1.00
        AFTER LOCK-OFF: (Elongation between wedges x 1.00) – Live End Anchor Set

        In both cases, Elongation between wedges (“E”) is elongation before Anchor Set (i.e., wedge seating loss is not included) obtained from your office software calcs or hand calcs whichever you use. it is the theoretical. It should be close to PL/AE, more or less, but not exactly because your friction, wobble, seating affecting the real deal.
        You put the above in a tabulaated format (with stressing sequence if any) and give it to your field crew. The above calculations are the target elongations they should be measuring.

        I hope that helps

        NOTE: By the way, i am considereing a career in Dubai. If you know anyone needing a pt engineer, pass the word.

        Disclaimer: The above is valid for a typical stand-alone bridge I-girder and shall not be understood as a general procedure for every PT sceneraio. Every case is different and shall be considered and analyzed as such.